If you write a lot of programs, and you're used to squeezing them all the time, you find that it's easy to write a program that's simple. A lot of it is having a clear sense of what you want to say — writing the proof by choosing what to prove, and being clear about that. In programming, a lot of simplicity comes from knowing what matters and what doesn't matter.
A Conversation with Ward Cunningham (2003) - The Simplest Thing that Could Possibly Work